The New York City Buildings Department now recognizes structural designs using high strength Grade 100 concrete reinforcing steels. Through issuance of Buildings Bulletin 2015-036, Irvine, Calif.-based MMFX Steel Corp. of America notes, the city accepts designs employing the 100,000-psi yield strength of ASTM A1035/A1035M-15 rebar. The document clears the way for MMFX high strength ChrõmX rebar in a market ushering a wave of active or proposed tower projects whose slender profiles invite reinforced concrete design—owing especially to stiffness characteristics tempering sway.
High strength steel reinforcement specs enable designers to address costly rebar congestion problems in such projects and expedite building delivery. Using high strength Grade 100 rebar such as ChrõmX 2100 (ASTM A1035) in lieu of conventional alternatives, MMFX contends, allows for a reinforcing steel volume reduction up to 40 percent in high rise building engineering, and lowers fabrication and placement costs up to 60 percent. Additional efficiencies, plus cost and time savings, loom in construction design, where high strength rebar affords streamlined shear walls and columns or shallower mat foundations.
“ASTM A1035 is now the only 100 ksi reinforcing steel allowed in any New York structure, the only reinforcement over 80 ksi that can be used in beams and slabs, and the only 100 ksi reinforcement that can be used in Seismic Design Categories A, B and C,” says MMFX CEO Thomas Russo. “Designing at these higher strengths using this new bulletin and ChrõmX (A1035) rebar will result in up-front construction cost savings, as well as increased construction efficiencies and eased logistics, benefiting contractors, developers and city residents.”
Buildings Bulletin 2015-036 allows designs up to 100,000 psi yield using ASTM A1035 reinforcement in accordance with ACI 318, as modified by ACI ITG 6R-10 and ICC-ES AC429. New York City joins such markets as Miami and Seattle where engineers are already applying code-sanctioned high strength rebar designs in high rise towers.
REINFORCING STEEL MILESTONES
As part of its Long Term Bridge Performance Program, geared to studying and collecting field data on structures completed since 1960, the Federal Highway Administration has delivered its first timeline tracking materials progress, “National Changes in Bridge Practices for Reinforcing Bars.” With National Concrete Bridge Council input, the timeline traces specifications from 1910 through 2015, and calls out development of specialty reinforcements to address issues related to corrosion and/or higher tensile strength. Specialty reinforcing bars include epoxy-coated, galvanized, dual-coated, and stainless steel.
Most recently, the document cites the issue of new or fully revised standards: ASTM A775, Standard Specification for Epoxy-Coated Steel Reinforcing Bars; ASTM D3963/D3963M, Standard Specification for Fabrication and Jobsite Handling of Epoxy-Coated Steel Reinforcing Bars; and, ASTM A1094/A1094M, Standard Specification for Continuous Hot-Dip Galvanized Steel Bars for Concrete Reinforcement. It also references ASTM A1035/A1035M, Standard Specification for Deformed and Plain, Low-Carbon, Chromium, Steel Bars for Concrete Reinforcement, to which have been added types CL and CM, available in grades 100 and 120 and formulated with lower chromium contents than the current type CS.